Note: Descriptions are shown in the official language in which they were submitted.
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VIBRATORY MILLING MACHINE HAVING LINEAR RECIPROCATING
MOTION
FIELD OF THE INVENTION
This invention relates to milling eduipment, and more particularly to a
vibratory milling machine for removing rock or cementitious material in a
substantially linear reciprocating motion.
BACKGROUND OF THE INVENTION
In the milling of rock and cementitious materials, it is often required to
remove large alnounts of material, including hard mineral deposits, fairly
rapidly. Machines have been proposed for this pulpose in order to increase
productivity and reduce labor costs over manual methods. Many such proposed
tools have used oscillation in combination with other motions, such as in a
rotating 1111n111g tool, to cut rock with less energy than otherwise would be
required. Attempts to produce a machine using these concepts have met with
limited success, however, due to the destructive nature of oscillation forces.
Another sitz.iation in whicli oscillation has been used to enhance the
machining of rock is in drilling operations, such as core drilling througll
rock
forlnations. Devices proposed for this purpose have used a pair of counter-
rotating, eccentrically-weighted cylinders to create vibrational forces in the
direction of a drill string. Such mechanisms remain free to move in directions
other than tlie direction of the drill string, however, and tllerefore resLdt
in
destructive oscillations, as well. Tllus, it is desirable to provide a
vibratory
nlilling machine capable of rapidly removing rock or cemetitious material and
yet having a long usefiil life.
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SUMMARY OF THE INVENTION
The present invention confines a vibratoiy housing to substantially
linear reciprocating movement relative to a base, causing a tool carried by
the
housing to impact a mineral fonnation or other work piece substantially in a
primary milling direction. The vibratory motion is generated by two or more
eccentrically-weighted rotors rotated by a conunon drive mechanism. The
rotors are preferably arranged in pairs with the rotors of each pair rotating
in
opposite directions about parallel axes so that lateral oscillations cancel
and
longitudinal vibrations in the milling direction are maximized. When the
rotors
of this mechanism are rotated at a rate of 3000-6000 revolutions per minute
(rpin), a milling tool car-ried by the housing is subjected to linear sonic
vibrations in the range of 50-100 hertz. This facilitates the renioval of
material
by the milling tool on a continuous basis.
The size of the inilling machine is kept to a minimum by providing
hydrostatic fluid bearings between the outer surfaces of the rotors and the
housing itself. In one enlbodiment, the lubricant for these bearings is
conducted
through the housing and associated bearing inserts to the surface of the
rotor.
Thus, the vibratory milling machine and method of the invention
include: a base; a housing supported by the base for substantially linear
reciprocating movement relative thereto in a milling direction; at least two
rotors mounted for rotation relative to the housing substantially about
respective primary axes, each of the rotors having an asynunetrical weight
distribution about its primary axis for imparting vibratory forces to the
housing
as the rotor rotates; a drive structure for rotationally driving the rotors;
and a
milling tool carried by the housing for reciprocating movement against a work
piece substantially in the milling direction. In one embodiment, the milling
machine has at least one pair of rotors positioned side-by-side in the housing
with their primaiy axes on opposite sides of a central plane. The rotors of
each
pair are then synchronized with one another and rotate in opposite directions,
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and in phase, about their primary axes. In another einbodiment, the rotor has
a
cylindrical outer surface and a pressurized fluid bearing is disposed between
the rotor and the housing within which it rotates.
These and other aspects of the invention will be more readily
comprehended in view of the discussion herein and the accompanying
drawings wherein similar reference characters refer to similar elements.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a vibratory inilling machine constructed in
accordance witll an embodiment of the invention, the milling machine being
mounted to a support arm of a conventional back hoe or other piece of
excavating equipment.
FIG. 2 is an isometric view of the vibratory milling machine of FIG. 1 removed
from the support arm;
FIG. 3 is a bottom plan view of the vibratory milling machine of FIG. 2;
FIG. 4 is a cross-sectional view talcen along the line 4-4 of FIG. 3.
FIG. 5 is a front elevational view of a milling head of the vibratory m.illing
machine of FIG. 2, shown separated from its base and with a pair of side
covers
of the milling head broken away to show the gear trains underneath;
FIG. 6 is a left side elevational view of the milling head of FIG. 5 with the
corresponding side cover removed to illustrate a gear train underneath;
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FIG. 7 is a right side elevational view of the milling head of FIG. 5 with the
corresponding side cover removed to show the synchronizing gear train
undenieatl-i;
FIG. 8 is a somewhat stylized isometric view of the rotors, gear trains and
motors of the milling head of FIGS. 1- 7;
FIG. 9 is a somewhat diagranvnatic vertical cross-sectional view of one of the
rotors of FIG. 8 shown within a fragmentary portion of the housing, the
clearances between the journal and the bearing being exaggerated to show the
oil flow within the hydrodynamic journal bearing;
FIG. 10 is a somewhat diagrammatic view of the rotor of FIG. 9 showing in
vector form the lubricant pressures within the bearing structure;
FIGS. 11A, 11B, 11C and 11D are sequential diagranunatic representations of
the rotor of Figures 9 and 10 as it passes through one revolution of its
rotational
motion.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Referring now to the drawings, and particularly to FIGS. 1-4, a vibratory
milling machine' 10 constitiicted according to an embodiment of the invention
has a milling head 12 that oscillates in a substantially linear reciprocating
fashion relative to a base 14 to drive a milling tool 16 against a rock
formation,
mineral deposit or other hard worlc piece (not shown). The vibratory milling
machine 10, and tlius the milling tool 16, are moved against the worlc piece
by
a support arm 18 of a conventional back hoe, hydraulic excavator or otber
piece
of excavating equipment that carries the milling machine. As shown in FIG. 4,
the milling head 12 is subjected to vibratory forces by rotors 20 arranged in
pairs to rotate synchronously in opposing directions so that lateral
oscillations
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cancel and longitudinal oscillations in a nlilling direction 22 are
reinforced. As
illustrated in FIGS. 2 and 3, movement of the milling head 12 relative to the
base 14 is physically limited to the milling direction 22 by a slide mechanism
24. In addition, a buinper system 26 is provided at the upper end of the
milling
head 12 to limit the milling head 12 to a relatively short pre-defined range
of
travel in the milling direction.
Referring now primarily to Figures 4 and 8, the milling head 12 in the
illustrated embodinlent has six rotors 20 arranged in three pairs which are
disposed vertically relative to each other such that each pair of rotors has
one
rotor on either side of a central plane 30 extending vertically tlirough the
milling head 12. Each of the rotors 20 is mounted for rotation within a
cylindrical recess 34 of a housing or "block" 32 about a corresponding primary
axis 36. Each cylindrical recess 34 is lined with a pair of babbet-type
bearing
inserts 38 such that the outer cylindrical surface of the corresponding rotor
20
serves as a bearing journal. As described below, the bearings formed between
the outer journal surfaces of the rotors 20 and the iiuler surfaces of the
bearing
inserts 38 are pressure-lubricated by oil or other suitable h.ibricant
introduced
radially inwardly through passages 39 (FIG. 9) within the housing 32 and
between the bearing inserts 38, toward the outer jounlal surfaces of the
rotors.
The lubricant tlnis at least partially fills an aiuiular space 41 between the
outer
journal surfaces of the rotors 20 and the inner surfaces of the bearing
inserts 38,
creating a hydro-dynainic journal bearing capable of withstanding the
substantial vibrational forces created during operation of the milling machine
10. In addition, thrust washers 37 are provided at the ends of the rotors.
These washers bear against outer ends of the bearing inserts which protrude
(not shown) from the housing 32 to for111 t1lrUst bearings for the rotors.
Vibrational forces are created by rotation of the rotors 20 due to the
asynunetric weight distribution of each rotor about its primary axis 36. As
illustrated in FIG. 4, each rotor has four length-wise openings 40 extending
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through it and arranged syinmetrically about the axis 36 for reception of
cylindrical weights 42. In the illustrated embodiment, two of the openings 40
of
each rotor 20 are filled with cylindrical weights 42 and the other two
openings
are left empty. This causes each of the rotors 20 to be highly asynunetrical
in
mass, maximizing the vibrational force created by its rotation. The
cylindrical
weights 42 may be made of tLingsten or other suitable material of high mass.
As illustrated in FIG. 4, rotors 20 of each pair rotate in opposite
directions about their parallel axes and the weights 42 are positioned in
their
openings 40 such that the heaviest portions of the two rotors rotate "in
phase",
with each pair of rotors being synchronized such that all six of the rotors
are in
phase with each other. Thus, the lateral (i.e., perpendicular to the central
plane
30) vibrational force created by one of the rotors 20 is precisely cancelled
by an
equal and opposite vibrational force created by the other rotor of the same
pair.
Lateral vibrations are neutralized in this way as the rotors 20 rotate
synchronously within the housing 32, leaving only the longitudinal components
of the vibrational forces to act on the main housing 32: This causes the
vibrational forces of the milling head 12 to be channelled almost entirely
into
longitLidinal forces coinciding with the milling direction 22, resulting in
reciprocal movement of the milling head 12 relative to the base 14 by
operation
of the slide mechanism 24.
As shown in FIGS. 2 and 3, the slide mechanism 24 is made of a wear
plate 46 that slides longitudinally along a pair of chamlels 48 formed by
clamping bars 50 attached to the base 14. The wear plate 46 is attached to the
housing 32 through a slide base 52. Thus, the slide mechanism 24 prevents
undesirable lateral motion of the milling head 12 relative to the base 14 that
might otherwise result from the high vibrational energy imparted to the
milling
head 12, and yet allows the milling head to move freely in the longitudinal,
milling direction 22.
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The details of the bumper system 26, that maintains the milling head 12
within a prescribed range of motion relative to the base 14, are illustrated
most
clearly in FIG. 4. In the illustrated embodiment, the bumper system 26
includes
two pairs of bumpers 56 disposed on either side of a plate 58 of the base 14
such that respective bumper assembly bolts 60 extending downwardly tluough
the bumpers and threaded into the main housing 32 serve to resiliently mount
the main housing to the base. Each of the bumper asseinbly bolts has an
integral washer-like flange 62 at its upper end and a shank portion 64
extending
through the two washers and the plate 58 to a shoulder 66 and a reduced-
diameter portion 68 which is threaded into the main housing 32. The bumper
assembly bolts 60 are dimensioned to be threaded into the main housing 32
until they seat against the housing at the shoulders 66 to pre-compress the
buinpers 56 by a preselected amount. Thus, the dimensions and make-up of the
buinpers 56, as well as the dimensions of the bumper assembly bolt 60, can be
modified to alter the spring constant and the extent of travel of the milling
head
12 relative to the base 14.
The maiuler of synchronously driving the rotors 20 is seen most clearly
in FIGS. 5-7, wherein a pair of motors 70 drive the tliree rotors on the right
hand side of FIG. 6 through a pair of drive gears 72 on the output shafts of
the
motors which engage driven gears 74 carried by the rotors. Thus, for a
clockwise rotation of the motors 70, as viewed in FIG. 6, the rotors on the
right
hand side of FIG. 6 will rotate in a counter-cloclcwise direction. As seen in
FIG.
7, timing gears 76 are carried at the other ends of each of the rotors 20 such
that
the timing gears 76 of each pair of rotors engage each other. This causes the
non-driven row of rotors (i.e., the row of rotors on the left hand side of
FIG. 6)
to rotate in a direction opposite to the first row of rotors which are driven
directly by the motors 70. Thus, the operation of the gears 72 and 74 on the
motor side of the milling head 12, along with the timing gears 76 on the back
side of the milling head 12, serve to synclironize all six of the rotors 20
such
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that they all rotate at the same speed and in the same phase with the two
vertical rows of rotors rotating in opposite directions.
As seen in FIG. 5, a side cover 78 covers the gear train on the motor side
of the milling head, while a side cover 80 covers the timing gears 76 on the
opposite side of the milling head. These two covers protect the gear trains
and
keep them clean while at the same time containing lubricant circulating within
the milling head. In addition, a plurality of seals (not shown) may be
provided
on the motor side of each of the rotors to maintain lubricant pressure within
the
journal bearings. It will also be understood that additional bearings (not
shown)
may be provided at either end of the rotors 20 to facilitate their rotation
relative
to the main housing 32 when sufficient lubricant pressure is not available;
however, the primaiy bearing fiulction will nevertheless be served by the
hydrodynamic journal bearings between the rotors and the main housing 32.
Tuiiiing now to Figures 9-11, the characteristics of the oil film between
each of the rotors 20 and its coiTesponding bearing insert 38 are crucial to
the
operation of the hydro-dynamic journal bearings and the usefi.illife of the
milling head 12. As shown in Figure 9, in the illustrated embodiment, oil or
other lubricant enters the cylindrical recess 34 of the housing 32 through the
passages 39 and is conducted radially inwardly through a gap between the
bearing inserts 38 to the space 41. The lubricant flows through the space 41
in a
direction parallel to the rotors 20, and ultimately out through the thrust
bearings
at the ends of the rotors.
The pressure of the lubricant between the rotor and the bearing insert is
illustrated schematically in FIG. 10 for a clockwise rotation of the rotor.
The
outwardly directed arrows of the pressure distribution 92 indicate a high
positive pressure of the lubricant, whereas the inwardly directed arrows of
the
pressure distribution 94 indicate low lubricant pressure. Thus, as the rotor
rotates within the insert 38, lubricant "whirls" just ahead of the point of
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maximum centrifiigal load, causing the interface between the rotor and the
bearing insert to be well lubricated where the load is felt most acutely. This
"whirl" is shown in FIGS. 11A, 11B, 11C and 11D, which together represent
sequential points in a single rotation of the rotor.
In the course of rotation, the primary axis of the rotor moves about its
original location, defining a small circle near the center line of the bearing
insert. This path of the rotor's axis is illustrated at 96 in FIG. 10. In one
embodiment, the diameter of this circle is on the order of .006 to .008
inches.
Of course, all of the clearances between the journal surface of the rotor 20
and
the internal surface of the bearing, as well as the patli 96 followed by the
geometric center of the rotor, are exaggerated in FIGS. 9-11 for clarity. In
order to accominodate this motion of the rotors' geometric centers, the drive
gears 72, the driven gears 74, and the timing gears 76 are provided with
adequate backlash to permit the eccentric motion without binding.
The structi.ires of the support arm 18 and the base 14 are illustrated most
clearly in FIGS. 1-3, wherein the base 14 is illustrated as a heavy weldment
made of high-strength steel able to withstand the extremely high forces
created
in automated milling operations. As illustrated in FIGS. 2 and. 3, the base 14
is
provided with a pair of bosses 98 for receiving a pivot pin or bolt 100 to
pivotally attach the base 14 and support arm 18 of a back hoe or otlier piece
of
excavating equipment (not shown) with which the milling machine 10 is used.
The base 14 is also provided with a pair of bosses 102 at a point displaced
from
the pivot pin 100 for actLiation by an hydraulic ram 104 that itself is
anchored
to the support arm 18. Thus, as the support arm is moved, the vibratory
milling
machine 10 can be moved to any desired location so that the milling tool 16
contacts the rock or other worlc piece being machined. When it is desired to
change the orientation of the milling machine relative to the support arm, the
hydraulic ram 104 can be actuated. This places the operator in complete
control
of the orientation and use of the milling machine 10.
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The various elements of the milling machine 10 may be made of a wide
variety of materials without deviating from the scope of the invention. In one
embodiment, the base 14, the milling head 12, the rotors 20 and the clamping
bars 15 are made of high-strengtll steel, while the wear plate 46 of the slide
mechanism 24 would be of a softer, dissimilar material such as a bronze alloy,
nylon or a suitable fluorocarbon polymer of the type marlceted by Dupont under
the trademark, Teflon. The babbet-type bearing inserts 38 may also be made of
a variety of materials, however in one embodiment they are steel-backed
bronze bearing inserts of the type used in the automotive industry. One such
bearing insert is a steel-backed bushing marlceted by Garlock under the
designation DP4 080DP056. These particular bushings have an inside diameter
that varies between 5.0056 and 4.9998 inches. In this embodiment, due to the
wide tolerance range, the rotors may be finished to the actual size required
after
the bushings are installed in the housing. The finish on the resulting outer
cylindrical surface of the rotors 20 may also be given a texture, such as that
of a
honed cylindrical bore, to maximize bushing life and oil film thickness. The
cylindrical weights 42 within the rotors 20 may be tLuzgsten carbide or other
suitable material having suitable weight and corrosion-resistance properties.
In another einbodiment, the clearance between the rotor's outer surface
and the inner surface of the bearing inserts is between 0.008 and 0.010
inches.
The minimum calculated lubricant film thickness at 4500 revolutions per
lninute is then between 0.00179 and 0.00194 inches. Oil flow through each
bearing may be 2.872 to 3.624 gallons per minute, for a total of 34.5 to 43.5
gallons per minute for the entire machine. Power loss per bearing at 4500
revolutions per minute is calculated as 9.579 to 9.792 horsepower or 115 to
118
horsepower total. Temperature rise tllrough the bearings is then between 32
and
41 degrees Fahrenheit, for a total heat load of 4900 to 5000 BTUlminute from
the bearings. Oil scavenge is through a 2.00 inch port (not shown) in one of
the
housing side covers 78 or 80.
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In still another embodiment, the hydraulic motors 70 and the various
gear sets may be selected to cause the rotors to spin in a range of between
3000
and 6000 revolutions per minute. This corresponds to a frequency of movement
of the milling head 12 between 50 and 100 hertz. Thus, in such an embodiiuent,
the milling tool 16 would be actLiated at sonic frequencies against rock or
other
mineral deposits to machine material away in a milling operation.
Although certain exemplary embodiments of the invention have been
described above in detail and shown in the accompanying drawings, it is to be
understood that such einbodiments are merely illustrative of, and not
restrictive
of, the broad invention. It will thus be recognized that various modifications
may be made to the illustrated and other embodiments of the invention
described above, without departing from the broad inventive concept. In view
of the above it will be understood that the invention is not limited to the
particular embodiments or arrangements disclosed but is rather intended to
cover any changes, adaptations or modifications which are within the scope and
spirit of the invention as defined by the appended claims. For example, the
llydro-dynamic journal bearings of the invention can be replaced by mechanical
bearings such as packed or permanently lubricated ball or roller bearings, if
desired. Likewise, the frequency of operation and the physical arrangement of
the rotors can be altered depending on the application being addressed.
